Antimicrobial activity of some pyrimidine derivatives in DMF and DMSO

. A series of pyrimidine derivatives have been synthesized and their structures were confirmed by IR, 1 H NMR and mass spectral data. All these synthesized compounds were tested in vitro for their antimicrobial potential against Gram positive, Gram negative strains of bacteria as well as fungal strains in N, N-dimethyl formamide and dimethyl sulfoxide.

In the present work, some novel pyrimidine derivatives were synthesized. The characterization of synthesized compounds was done by IR, NMR and mass spectral analysis.
The antimicrobial activity of the synthesized compounds was done against some pathogenic Gram positive and Gram negative bacteria and fungi in N, N-dimethyl formamide and dimethyl sulfoxide.

Synthesis: Synthesis of Int-I (2-(benzo[d]thiazol-2-yl) acetonitrile):
To the ethanolic solution of 2-amino thiophenol (0.1 mol), malono nitrile (0.1 mol) was added at 0-5 0 C temperature, and glacial acetic acid was added drop wise. By the removal of ammonia gas, cyclized product was formed (Int-I). The completion of reaction was confirmed by analytical thin layer chromatography (TLC) using (0.75 : 0.25 Hexane : Ethyl acetate) as mobile phase. The resulting product was filtered, washed with hexane and dried under vacuum. This product was used further in next step.

Synthesis of pyrimidines:
In DMF solution of above synthesized product (Int-I), different substituted aldehydes and guanidine hydrochloride were added. The reaction mixture was refluxed for 8-10 hrs at 145-150 0 C using piperidine as catalysis.. The complecation of reaction was confirmed by analytical thin layer chromatography (TLC) using (ethyl acetate) as mobile phase. After complication of reaction, the reaction mixure was washed with diethyl ether in order to remove non polar impurities. The resulting solid was filtered.
The physical constants of synthesized compounds are shown in Table 1.
The structure confirmation of these crystallized compounds was done by FTIR, 1 H NMR and mss spectral data. IR spectra were recorded on IR affinity 1S (furrier transport infra-red spectroscopy), 1 H-NMR spectra were taken on a Bruker AVANCE II 400. In all the cases, 1 H NMR spectra were obtained in DMSO-d 6 using TMS as an internal standard. The NMR signals are reported in δppm. Mass spectra were determined using direct inlet probe on a GCMS-QP-2010 mass spectrometer.

Preparation of solutions of compounds:
For all the compounds, DMF and DMSO were used for screening of antimicrobial activity. The solution of 20 mg/ml concentration was prepared for all the compounds.

RESULTS AND DISCUSSION:
In total, 10 compounds (AMG-1 to AMG-10) were synthesized. Table 1 shows the physical parameters of these compounds. The IR, 1 H NMR and mass spectra of compound AMG-2 are shown in Figures 1, 2   Antibacterial activity: Figure 4 shows the zone of inhibition of synthesized compound against Gram positive bacteria in DMF and DMSO. In DMF (Figure 4[A]), against BC AMG-5 exhibited maximum inhibition and minimum is shown by AMG-4. The compounds AMG-1, AMG-6 and AMG-8 showed moderate inhibition against BC. Other compounds had no effect at all. In DMSO, against BC, AMG-1 had maximum inhibition whereas minimum inhibition is due to AMG-6. Some of the compounds had no effect all against BC. The results suggest that inhibition depends not only on structure of compounds but also on the solvent. Against BC, in DMF, maximum compounds had inhibition as compared to DMSO. So, for this strain, DMF is more effective. The comparison of inhibition among different compounds shows that all the compounds have the same central moiety but different substitution groups. In DMF, AMG-5 containing 4-methoxy group showed maximum inhibition against BC. The compound AMG-8 also contains methoxy group but at 3 rd position but its effect is less as compared to AMG-5. This suggests that position of group also affect inhibition. In DMSO, against BC AMG-1 containing 4-chloro group had maximum effect but when chloro group is at 3 rd position as in AMG-3, it had no effect at all.
Against SA, AMG-6 exhibited maximum inhibition in DMF whereas AMG-3 had minimum inhibition. Other compounds showed moderate inhibition except AMG-5 and AMG-8. Thus, in DMF against this strain 4-fluoro group is very effective whereas methoxy group at 3 rd and 4 th position had no effect at all. However, in DMSO against SA, only AMG-1, AMG-5, AMG-6 and AMG-9 showed inhibition and maximum is exhibited by AMG-6 containing 4-fluoro group. The comparison of inhibition against this strain in the two solvents again suggests DMF to be good solvent.
For LM, not a single compound was effective in DMF whereas in DMSO, only AMG-5 exhibited inhibition.
All over, AMG-6 (containing 4-flouro group) could inhibit 75% of Gram positive bacteria in DMF solvent and AMG-5 could inhibit 100% the zone of inhibition in DMSO solvent. Thus overall, AMG-5 having 4-OCH 3 substitution is more effective for studied Gram positive bacteria in both the solvents and DMF is good solvent for the studied Gram positive bacteria. Figure 5 shows zone of inhibition against Gram negative bacteria in DMF and DMSO. Only AMG-2 and AMG-3 containing 3,4-dimethoxy and 3-chloro groups respectively inhibit EC in
In DMF, AMG-4, AMG-8 and AMG-9 showed inhibition against KP and maximum inhibition is by AMG-4 containing 4-bromo group. None of the compound could inhibit KP in DMSO.
Thus, among studied Gram negative bacteria, for the studied compounds, DMSO is better solvent and KP is the most resistant bacteria. Further, the studied compounds are found to be not as effective against Gram negative bacteria as compared to Gram positive bacteria.
The zones of inhibition against four fungal strains are shown in Figure 6 for all the compounds in DMF and DMSO. Not a single compound could inhibit CG in both DMF and DMSO. Thus, CG is most resistant fungal strain among the selected fungal strains for the studied compounds.
All the studied compounds show moderate activity against CE in DMF whereas only AMG-5 containing 4-methoxy group inhibited CE in DMSO. So, -OCH 3 group at 4 th position is more effective for CE in DMSO. Whereas all the groups are effective in DMF.
Except AMG-8 and AMG-9, all the studied compounds showed inhibition against CA in DMF. Whereas only AMG-4 and AMG-5 could inhibit CA in DMF. Against CN, all the compounds except AMG-4, AMG-5 and AMG-10, exhibited inhibition in DMF. However, in DMSO, only AMG-3 and AMG-5 could inhibit.
AMG-5 and AMG-6 having 4-OCH 3 and 4-F substitution respectively. AMG-5 could inhibit 75% zone of inhibition in both the solvents. AMG-6 could inhibit 75% of the studied fungal strains in DMF whereas in DMSO, this compound had no effect at all.
Again, for the studied fungal strains, DMF is better solvent.

CONCLUSION
It is concluded that inhibition depends on solvent used, molecular structure of compound and bacterial strain. Overall, DMF is better solvent for the studied compounds and compounds containing methoxy group is most effective. Thus, such compound can act as lead molecule for the synthesis of new therapeutic drug.